1. Field of the Invention
The present invention relates to a display device such as a monitor used in a personal computer (hereinafter referred to as a PC) or the like, and particularly relates to an information processing unit having portability, such as a notebook PC.
2. Description of Related Art
Recently, a portable information processing unit such as a notebook PC has faced contradictory requirements: the improvement of resistance against an external force such as an impact when dropped or a static pressure, and the reduction of size and weight. An effective means of achieving the reduction of weight is to decrease a wall thickness of a casing. When a casing has a smaller wall thickness, however, the mechanical strength thereof decreases. JP 9(1997)-62400 A discloses a casing that is provided with reinforcing ribs over a front-side internal face in order to increase the mechanical strength, the reinforcing ribs being extended diagonally toward the inside. JP 2007-272860 A discloses a structure as follows: in order to increase the mechanical strength of a casing having a domed structure, reinforcing ribs that are substantially parallel in a direction in which a portion is raised for forming the domed structure are provided on internal surfaces of the casing.
A configuration in which diagonal reinforcing ribs are provided over a front-side internal face, as disclosed by JP 9(1997)-62400 A, has the following problem: in the case where an area of a casing is increased, such as the case where the area of the casing is increased as a screen size is widened, diagonal ribs increase for the increase in the area of the casing. In other words, there is a problem that a weight unavoidably increases in proportion to the area. Further, what usually is carried out in order to make the thin-walled casing resistant against an external force is to use a metal material. Still further, in the manufacturing aspect, so-called casting, in which a molten metal material is poured into a die and molded by casting, is preferable from the viewpoint of volume production. In the case where an approximately rectangular casing is formed by molding, usually a molten metal flows from one side forming a perimeter of the casing toward another side opposite thereto, and thereafter is cooled. The diagonal ribs disclosed by JP 9(1997)-62400 A, however, are formed in directions crossing the direction in which the molten metal flows (hereinafter this direction is referred to as a flow direction), and therefore the flow is hindered. This causes, for example, the molten metal to be supplied insufficiently to a downstream part with respect to the ribs in the flow direction, thereby making it difficult to achieve uniform molding. Particularly, in the case where a metal having a high melt viscosity or a metal that is easily solidified when cooled is used, it is difficult, or substantially impossible in fact, to mold a casing having ribs crossing the flow direction.
Further, as to the casing disclosed by JP 2007-272860 A, there is a possibility that ribs could come into contact with a display part when the raised part deforms in response to a static pressure applied to.